The invention relates to directional RF couplers.
It is a common practice in the radio frequncy transmission art to use directional couplers in transmission lines to sample forward and reflected voltages on the transmission line. For example, they are often placed between a power amplifier as part of a feedback control loop to stabilize power amplifier output level under differing environmental conditions and to reduce output power in the case of a severe impedance mismatch which could cause overheating and consequent destruction of the power amplifier output devices. The latter is particularly important with modern solid state power amplifiers.
The requirements of the modern user of RF transmitting and receiving equipment dictate that RF devices, includng directional couplers, be extremely broad banded. Typical requirements of military users having electronic countermeasures and electronic counter-countermeasures applications are a bandwidth of six (6) octaves. Otherwise, multiple RF units would have to be used which would require time consuming switching and impedance matching operations and would increase the size, weight, and cost and lowr the reliability of such systems. Prior art directional couplers using transformers with metal cores or transmission line techniques are limited to a fairly narrow frequency range.
It is therefore an object of the present invention to provide an RF directional coupler having an extremely wide banwidth exceeding a 25:1 frequency range.
It is another object of the present invention to provide a broad band directional coupler having a high power handling capability.